Drum filters have extensive applications in filtering washer fluids and coolants for machining operations. Drum filters generally comprise a perforate drum encircled by a permanent media belt. Fluid flows gravitationally from the outside of the drum through the media belt to the inside thereof. The fluid is then discharged from inside the drum by drainage through a central opening to, for example, a fluid holding tank. A drum filter of this type is exemplified by U.S. Pat. No. 5,112,485 to Hirs.
One problem inherent in prior art drum filters heretofore known and used is that gravitational flow limits the filter""s ability to draw fluid into the drum when filtering highly pressure-resistant contaminants. Stated another way, prior art drum filters have difficulty operating at pressure differentials between the interior and exterior of the drum greater than gravity.
U.S. Pat. No. 3,206,030 to Estabrook exemplifies a prior art filter that utilizes a pump to provide pressurized fluid flow through the filter media. However, the prior art vacuum drums require that the fluid flow through the filter be stopped when fresh media is advanced onto the filter drum, thereby requiring an interruption in the filtration process when contaminant loading becomes heavy.
The aforesaid problems are solved, in accordance with a preferred constructed embodiment of the present invention, by a drum filter disposed in a contaminated fluid tank having a tubular shaft for withdrawing filtered fluid connected to a pump to produce a relatively high pressure differential across the filter drum. The pressure differential is enhanced by a novel filter drum having both perforate and imperforate sections. The perforate section is disposed below the level of contaminated fluid in a tank and the imperforate section is adjacent the perforate section at two points on the drum and rises above the level of contaminated fluid. A filter media belt encircles the entire perforate section of the drum to filter contaminated fluid being drawn into the interior of the drum by the suction of the pump. Rotation of the drum to supply fresh media thereto and actuation of a plurality of spray nozzles for cleaning the media belt are controlled by a vacuum switch disposed at a point on the suction side of the drum. A limit switch allows the drum to be rotated a single revolution at a time, so as to always position the imperforate section of the drum upwardly in the tank.